In my opinion, there is not much good material available. I have been working towards establishing a Gospel bass lesson/tutorial website, but it been a slow going project over the past two years, as I prepare content (blog posts, videos, transcriptions, etc.) with other commitments in life.
With that said, if available in your area, my first and foremost advice is to immerse yourself into the Gospel community via joining a church or community choir. You will learn far more via the said method than any online resource.
From my experience, most churches who are Gospel music-focused do not seek musical talent via Craigslist or other online resources, as it is usually a tight-knit community where pastors and other church leaders know the local musicians in the area and/or seek recommendations from trusted individuals. Therefore, it would be beneficial to make a list of churches to visit who do not have a bassist and talk to the minister of music. As a person who has relocated several times over the past 10 years, due to work transfers and opportunities, the aforementioned process has always worked for me.
Another possible option is to seek out a community choir, such as a local Gospel Music Workshop of America (GMWA) chapter. I presently play, off and on, for two different GMWA chapters in my state and find it a more feasible situation, as it is not usually an ongoing weekly commitment. Furthermore, as one of their most important functions is to promote Gospel music via education and training, many local GMWA chapters will host workshops that will provide an opportunity to meet other Gospel musicians (including national recording artists and their musicians), receive hands-on instruction, clarification about certain techniques, etc. One tip, organists are a very good resource to learn the role of a bassist in Gospel music and are more likely to provide mentorship to a bassist, especially if the individual helps supports their music ministry efforts, than other bassists in the community.
Lastly, but just as important, listen to Gospel music and learn songs by ear. Learning songs by ear will be necessary anyways if you play in a Gospel music environment, due to the fact that very few songs are codified via standard notion, tablature or video. In addition, most live Gospel music situations involve an aspect of uncertainty because a select portion of the songs played are commonly not planned or practiced in advance. Therefore, a good ear is necessary.
